Large quantities of paint of various kinds, including lacquers, varnishes, enamels, and certain specialty paints such as urethane-based paints, catalyzed two-component paints, base coat/clear coat combination paints, high solids enamels or lacquers, and the like, are used to coat finished products in industries such as automotive manufacture and the like. These paints, lacquers and varnishes are generally solvent-based; however, certain of these paints can be water-based. Some are considered low solids paints (i.e. materials containing about 20 to about 30% solids) while others are considered high solids paints (i.e. those containing above 50% solids).
These materials are generally sprayed onto the piece to be painted or coated in an enclosed area such as a paint spray booth. In this operation, substantial quantities of solvent and oversprayed paint are discharged into the spray booth and the air drawn therein. Paint spray booths provide a means for capturing and containing paint overspray components in a suitable liquid material.
Paint spray booths generally include a chamber, a duct system for passing air through the chamber, and a sump containing circulating liquid located in the bottom of the chamber which can be directionalized in the spray booth chamber to form a curtain of liquid to contact the over-sprayed paint particles and collect at least a portion thereof. The paint spray booth also contains a gas discharge means such as a stack for discharging excess air or gaseous material.
The liquid employed in paint spray booth applications is most preferably a hydrophilic material capable of removing solid particulates from the air. The liquid chosen is ideally economical, safe to use and capable of efficient and economical recycle and reuse. The hydrophilic material of choice typically is comprised of water to which various chemicals are added to provide detackifying properties. Water-based compositions are also desirable for their general ease and safe handling during operation and during spray booth clean-up and maintenance.
Various water-based treatment compositions have been proposed. Heretofore, oil-in-water formulations in which water, oil and various additives are combined to form a suitable emulsion have been employed as the hydrophilic liquid. The use of such oil-in-water emulsions is taught in U.S. Pat. No. 4,378,235, No. 4,396,405, No. 4,523,932, No. 4,563,199, No. 4,444,573, No. 4,544,026, No. 4,750,919, and No. 4,919,691.
These oil-in-water emulsions are generally weak alkaline emulsions which can be broken upon acidification. In order to reclaim such materials, a method such as that outlined in U.S. Pat. No. 4,919,691 to Patzelt can be employed in which predetermined amounts of spent emulsion are withdrawn from the paint spray booth for treatment. The emulsion is broken into separate organic, aqueous, and solid phases by adjusting the pH of the withdrawn portion to a level between about 3.0 and about 6.5; with even lower pH levels being employed in certain instances. At least a portion of the paint solids are recovered from the aqueous, organic and solid phases. The oil and other emulsion additives are, then, recovered for reuse in reformed emulsion material. At low pH levels, reaction can occur with the paint materials present in the emulsion material which can result in depolymerization of the paint materials and the evolution of formaldehyde and gaseous amines. In order to accomplish effective paint solid recovery, it has been necessary to employ less acid in combination with mechanical force to achieve effective breaks.
The use of oil-in-water emulsions has certain inherent difficulties. These emulsions are weak emulsions which are easily broken. In order to maintain the material in an emulsified state, it is necessary to employ emulsion stabilizing additives, paying close attention to composition pH, and in many instances, subjecting the material to continuous mechanical agitation. The oil-in-water systems are not highly effective solubilizing agents for paint solids. Thus, much study has been directed to finding additives which would enhance the emulsion stability and solubilizing power. Many of the patents previously enumerated provide various approaches for addressing some or all of the shortcomings inherent in oil-in-water emulsion systems.
Given the problems encountered with the various hydrophilic liquids previously available, there has been incentive for industry and manufacturers to either switch to alternative technologies or to develop some type of non-oil-based aqueous emulsion as an alternative treatment solution compatible with existing paint spray booth equipment. One such treatment solution is disclosed in U.S. application Ser. No. 07/790,650 which is currently pending before the United States Patent and Trademark Office and is incorporated by reference herein. The treatment solution disclosed therein consists essentially of a non-volatile hydrocarbon selected from the group consisting of alcohol esters, alcohol ester derivatives, and mixtures thereof, an emulsifying agent having an HLB value ranging from about 6 to about 40, and water. Such compositions have been found to exhibit a great capacity for containing paint either by solubilization, dispersion, or a combination of the two processes and are made up of chemically stable components which retain their effectiveness in composition for a protracted period of time.
While the alcohol ester paint overspray treatment composition is considered to be made up of components which could be easily separated and recovered, it has been found that oil-in-water emulsion recovery processes such as those disclosed in the Patzelt reference provide an unacceptably low percentage yield of reusable material. Unfortunately, much of the potentially reusable material remains contaminated with paint solids and the like. Furthermore, use of the process disclosed in the Patzelt reference on the aqueous emulsion of the present invention does not achieve the level of recovery efficiency desired.
Thus, it would be desirable to provide a process which would yield readily reusable organic products which can be easily reformulated with the necessary additives to form a recycled emulsion. It is also desirable to provide a process which would render paint solids in a form which could be easily disposed of or subjected to further post-treatment processes. It is also desirable to provide a process which can accomplish these objectives with a minimum of material addition.